Maszlan Ismail

A review of S-band antenna system G/T measurement technique

For any orbiting satellite mission, reliable communication link between satellite and ground receiving and transmitting station is very crucial as this is the only way satellite communicates with its operator. The key component within a ground receiving & transmitting station that enables this communication link is the antenna system. To ensure reliable communication, measurement of the antenna gain-to-noise temperature, G/T is often conducted in order to determine the performance of the antenna system. This measurement is even more crucial particularly for an antenna system that is responsible to provide telemetry, tracking and control to a satellite. In this paper, the measurement technique used to establish the G/T of ANGKASA S-band antenna system which includes the methodology and calculation of the figure is presented.

Estimating tropical rain attenuation on the Earth-satellite path using radar data

Radar-return echoes, known as ‘reflectivity’, are exploited in the course of estimating rain attenuation along a slant path. Relevant radar gates or ‘range bins’ are identified to correlate a specific satellite path. The reflectivity value of each range bin is converted to rainfall rate using established radar reflectivity values – rainfall rates, (Z–R relation). Specific attenuation is then derived for all associated range bins. The attenuation for each bin is the product of specific attenuation and its effective path length. The summation of attenuation endured by all range bins is inferred as the attenuation along the slant path. In this study, an X-band slant path rain attenuation was estimated using 2.85 GHz (S-band) Terminal Doppler Weather Radar (TDWR) data. A technique to estimate rain attenuation by exploitation of radar information is elaborated in this article. Comparisons between the radar-derived attenuation estimations and actual satellite signal measurements are also presented. The findings were verified by comparing the generated values to the directly measured rain attenuation from the Razak satellite (RazakSAT). Radar reflectivity data were obtained from Kuala Lumpur International Airport (KLIA) radar station operated by the Malaysian Meteorology Department (MMD). Preliminary findings using the most recent Z–R relation (i.e. the generated radar-derived rain attenuation estimations) appear to show lower values than the actual measurements.

Rain Fade Estimations for the X-Band Satellite Communication Link in the Tropics

The X-band satellite communication (satcom) has been conventionally set aside for military and government organizations. It is also commonly known as the military band. The attributes of an X-band satcom hardware are expected to be designed specifically for military operations and they are expected to differ very much to those of commercial frequencies. The satcom will be likely to be exclusively designed to support smaller, low powered, tactical terminals deployed across various theatres of operation. In addition, X-band link is also anticipated to offer a more substantial increased of system capacity due to its higher frequencies compared to the forerunner S-band and C-band. The X-band satcom technology is drawing growing interest from military users including of the Malaysian authorities. However, there are many aspects of X-band that are harder to realize than of those of at lower frequencies. X-band frequencies certainly have higher atmospheric propagation losses, higher RF losses, and certainly much severe signal degradation due to rain. It is would be in the best interest of the satellite designers and engineers alike to accurately appraise the challenges of an X-band satcom link especially in the case of tropical regions where heavy rains are copious whilst the required technological advancements are in pursuit.

Comparison of Radar Derived Rain Attenuation with the RazakSAT's X-Band Link Signal Measurement

Abstract—The preliminary analysis involving comparison between radar derived attenuation using an S-band meteorological radar and measured signal of RazakSAT’s X-band satellite link is presented. The radar data employed was attained from the Malaysian Meteorological Department’s (MMD) terminal Doppler weather radar installed strategically in the vicinity of Kuala Lumpur International Airport (KLIA). The X-band (8 GHz) satellite-Earth signals of Malaysian RazatSat’s collected at the National Space Agency (NSA) space center have been analyzed and studied. The vertical polarization S-band radar reflectivity information was used to calculate the likely rain attenuation along the RazakSAT satellite propagation paths. This was carried out by first converting the radar reflectivity values into rainfall rate using the established Z-R relations of Marshall-Palmer equation and, afterwards, by evaluating the slant path attenuation through the assimilation of the specific rain attenuation derived at the rainfall rate.